1. Field of the Invention
The present invention relates to a coplanar line filter configured with coplanar resonators provided upon a dielectric substrate, a duplexer, and a communication device using the same.
2. Description of the Related Art
FIGS. 22A through 22C illustrate an example of a configuration of a coplanar line filter using a conventional coplanar resonator. FIG. 22A is a plan view of the dielectric substrate, FIG. 22B is a bottom view thereof, and FIG. 22C is a side view thereof. Formed on the upper side of the dielectric substrate 1 are center electrodes 2a and 2b having open ends, and a ground electrode 3 following the sides of these center electrodes. In the diagram, the arrows represent the electric field distribution. Due to such a structure, the center electrode 2a and the ground electrode 3 serve as one coplanar resonator, and the center electrode 2b and the ground electrode 3 serve as the other coplanar resonator. Further, these two coplanar resonators are coupled electromagnetically, thereby acting as a filter formed of two stages of resonators.
Generally, coplanar resonators forming a filter can comprise short-circuit portions and can be disposed on a single plane of a dielectric substrate, so reduction in size can be realized by utilizing xc2xc wavelength resonators. However, the amount of leakage of the electromagnetic field distribution in the resonating mode out from the dielectric substrate may be relatively great, i.e., the effective dielectric constant tends to be low, so there has been a limit to the reduction in size that is available.
Also, as shown in FIGS. 22A through 22C, the electric field heads from the center electrodes toward the ground electrode on either side, so the electric field is concentrated at the ends of the center electrodes. Consequently, there has been a problem in that a high no-load Q cannot be obtained.
The present invention provides a coplanar line filter, duplexer, and communication device using the same, wherein reduction in size of the entire article is facilitated, and no-load Q is increased.
To this end, the coplanar line filter according to the present invention comprises: a dielectric substrate having an upper plane and a lower plane; a coplanar resonator provided upon the upper plane of the dielectric substrate, the coplanar resonator comprising a first center electrode wherein an end thereof is an open end, and a ground electrode with a predetermined gap provided from the first center electrode; a second center electrode provided on the lower plane of the dielectric substrate, formed so as to face the first center electrode through the dielectric substrate; and a perimeter electrode provided on the lower plane of the dielectric substrate, formed so as to face the ground electrode through the dielectric substrate.
As will become apparent from the later-described embodiments, the center electrode patterns on the upper and lower sides of the dielectric substrate are mutually electromagnetically linked so as to act as a ring resonator (a balanced resonator), so the resonance frequency decreases. On the other hand, the dimensions of the electrode patterns and the dimensions of the dielectric substrate for obtaining a predetermined resonance frequency are reduced.
Further, resonance mode electromagnetic fields facing in the upper and lower directions from the dielectric substrate reduces the deterioration of no-load Q (hereafter referred to as xe2x80x9cQoxe2x80x9d) due to the edge effect (electric-field concentration at the electrode edges), thereby obtaining a high Qo.
The duplexer according to the present invention comprises: a transmission filter comprising a coplanar line filter according to the present invention; and a reception filter comprising a coplanar line filter according to the present invention. Thus, high Qo and low insertion loss properties are obtained with an overall small size.
The communication device according to the present invention comprises one or more of the above filters or duplexer arranged for processing transmission signals or reception signals in a high-frequency circuit for example, thereby obtaining high electric usage efficiency properties with a small size.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings, in which like references denote like elements and parts.